This invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a semiconductor device in which an insulating substrate is mounted, in addition to a semiconductor pellet, on a bed of a lead frame, and a method of manufacturing such a semiconductor device.
In semiconductor devices, only one semiconductor pellet is ordinarily mounted on the bed of the lead frame. However, due to recent marketing demands, there have been many cases where a plurality of pellets are mounted within a single semiconductor device.
In such devices, for example, two semiconductor pellets are fixed on the bed of the lead frame by means of a conductive adhesive agent. Respective pads and inner leads of these pellets are connected through wires by wire bonding. In addition, it is required, in this case, to connect two pellets to each other.
However, when pellets are directly connected to each other by wire bonding, there is the possibility that the pads of the pellets may be damaged, and respective arrangements on the bed may be restricted. In view of this, an approach is employed to fix, on the bed between two pellets, an insulating substrate on which a wiring pattern is formed, to thus implement wire bonding to the two pellets through the insulating substrate.
In the case of fixing the insulating substrate onto the bed, an insulating adhesive agent was conventionally used. The insulating adhesive agent used here is mainly comprised of an epoxy resin including about 20% of silicon dioxide (SiO.sub.2) as a filling material. In addition, an additive agent is included therein. The percentage content of the filling material is generally selected to be between about 20% to 40% depending on the solubility of the silicon dioxide filling material into the epoxy resin.
However, when the filling rate is a low value of 20 to 40%, the hardness after hardening is disadvantageously insufficient when compared to that of typical silver (Ag) paste.
Furthermore, the epoxy resin has a characteristic such that its hardness is lowered at a high temperature because it is apt to be affected by temperature. For this reason, although it is required to essentially carry out wire bonding at a high temperature of about 270.degree. C., wire bonding using the above-mentioned insulating adhesive agent must be carried out at a temperature lower than 150.degree. C., resulting in the problem that a sufficient bonding strength between the wires and the insulating substrate cannot be provided.
In addition, in the case of an adhesive agent having a filling rate of less than about 60%, it is confirmed that there is apt to occur a bleed phenomenon such that such an adhesive agent goes round on the surface of the insulating substrate during the process of hardening. When the bleed phenomenon occurs, there are instances where the adhesive agent may adhere to pads on the insulating substrate. Thus, the wire bonding ability or characteristic is also considerably deteriorated.
As stated above, an insulating adhesive agent having a low filling rate was used from a viewpoint of solubility. However, the employment of such an adhesive agent disadvantageously results in insufficient hardness of the adhesive agent, and lowered wire bonding ability. As a result, high reliability cannot be provided.